Liquid crystal display devices have a small thickness, a light weight, and a low power consumption as characteristics, and are used in various fields. Display performance of such liquid crystal display devices is drastically improved year by year. As a result, recently the display performance of liquid crystal display devices has become superior to that of CRTs (cathode ray tubes).
A display mode of a liquid crystal display device is determined by how liquid crystal is aligned in a liquid crystal cell. Conventionally, various display modes are known as display modes of liquid crystal display devices. Examples of such display modes known are a TN (Twisted Nematic) mode, an MVA (Multi-domain Vertical Alignment) mode, an IPS (In-Plain Switching) mode, and an OCB (Optically Compensated Birefringence) mode. Liquid crystal display devices employing these display methods have been mass-produced conventionally.
Among the liquid crystal display devices of these various display modes above, for example, a liquid crystal display device employing the TN mode is generally used in a wide range.
However, a liquid crystal display device employing the TN mode has disadvantages such as a slow response and a narrow viewing angle.
The MVA mode (Refer to, for example, “K. Ohmuro, S. Kataoka, T. Sasaki, and Y. Koike, ‘Development of Super-High-Image-Quality Vertical-Alignment-Mode LCD’, SID 1997 Digest, No. 33.3, p. 845-848, 1997.” (hereinafter, referred to as “Non-Patent Document 1”) and “H. Yoshida, T. Kamada, K. Ueda, R. Tanaka, Y. Koike, K. Okamoto, P. L. Chen and J. Lin, ‘Multi-domain Vertically Aligned LCDs with Super-wide Viewing Range for Gray-scale Images’, Asia Display/IMID'04 Digest, No. 12.2, (2004).” (hereinafter, referred to as “Non-Patent Document 2”)) is a display mode according to which a fringe field is formed by providing a slit to each pixel electrode on an active matrix substrate and, further, providing a rib for controlling liquid crystal molecule alignment to a counter electrode on a counter substrate, thereby providing a plurality of alignment directions of liquid crystal molecules.
The MVA mode liquid crystal display device achieves a wide viewing angle by having a plurality of divisional directions (Multi-domains) in each of which liquid crystal molecules are tilted at the time when a voltage is applied. Further, employing a vertical alignment mode, the MVA mode liquid crystal display device can obtain a higher contrast as compared with liquid crystal display devices of other modes such as the TN mode, the IPS mode, and the OCB mode. However, the MVA mode liquid crystal display has disadvantages such that (i) a production process is complex and (ii) as with the TN mode liquid crystal display device, a response speed is slow.
Among the other display modes described above, the IPS mode (Refer, for example, to “R. A. Soref, ‘Field Effects in Nematic Liquid Crystals Obtained with Interdigital Electrodes’, J. Appl. Phys., Vol. 45, No. 12, p. 5466-5468, 1974.” (hereinafter, referred to as “Non-Patent Document 3”) and “R. Kiefer, B. Weber, F. Windschield, and G. Baur, ‘In-Plane Switching of Nematic Liquid Crystals’, Proc. The 12th Int'l Disp. Res. Conf. (Japan Display'92), No. P2-30, p. 547-550, 1992.” (hereinafter, referred to as “Non-Patent Document 4”)) is known as a display mode according to which a wide viewing angle is achieved by using a simpler configuration. Switching the liquid crystal molecules within a plane, the IPS mode liquid crystal display device has a very wide viewing angle. However, the IPS mode also has a disadvantage such that a response speed is slow as with the TN mode and the MVA mode. Further, the IPS mode is not suitable for mobile devices or in-vehicle devices for which a high speed at a low temperature is required.
Meanwhile, among the various display modes, the OCB mode (Refer, for example, to “P. L. Bos and J. A. Rahman, ‘An Optically “Self-Compensating” Electro-Optical Effect with Wide Angle of View’, Technical Digest of SID Symp., p. 273-276, 1993.” (hereinafter, referred to as “Non-Patent Document 5”) and “Y. Yamaguchi, T. Miyashita, and T. Uchida, ‘Wide-Viewing-Angle Display Mode for the Active-Matrix LCD Using Bend-Alignment Liquid-Crystal Cell’, Technical Digest of SID Symp., p. 277-280, 1993.” (hereinafter, referred to as “Non-Patent Document 6”)) is an only display mode that can achieve a high-speed response by using a simple configuration in which a nematic liquid crystal is merely sandwiched by two substrates having been subjected to alignment treatment in parallel directions. Therefore, the OCB mode is particularly spotlighted for in-vehicle applications in which a response characteristic at a low temperature may become a problem.
However, while exhibiting such a high-speed response, the OCB mode requires a transition operation from a splay alignment that is an initial alignment to a bend alignment in driving when power supply is turned on. Accordingly, the OCB mode requires an initial transition driving circuit in addition to an ordinary driving circuit. Therefore, a factor to increase cost is inherent in the OCB mode. Further, the OCB mode is inferior in a viewing angle characteristic to the MVA mode and IPS mode.
Other than the display mode as described above, another display mode is proposed for solving a process problem of the MVA mode. This display mode carries out driving by a lateral electric field in a vertical alignment mode, employing a p-type nematic liquid crystal as a liquid crystal material (Refer to, for example, Japanese Patent Application Publication, Tokukaishou, No. 57-618 (published on Jan. 5, 1982) (hereinafter, referred to as “Patent Document 1”), Japanese Patent Application Publication, Tokukaihei, No. 10-186351 (published on Jul. 14, 1998) (hereinafter, referred to as “Patent Document 2”), Japanese Patent Application Publication, Tokukaihei, No. 10-333171 (published on Dec. 18, 1998) (hereinafter, referred to as “Patent Document 3”), Japanese Patent Application Publication, Tokukaihei, No. 11-24068 (published on Jan. 29, 1999) (hereinafter, referred to as “Patent Document 4”), Japanese Patent Application Publication, Tokukai, No. 2000-275682 (published on Oct. 6, 2000) (hereinafter, referred to as “Patent Document 5”), and Japanese Patent Application Publication, Tokukai, No. 2002-55357 (published on Feb. 20, 2002) (hereinafter, referred to as “Patent Document 6”)).
In this display mode, while a high contrast characteristic due to vertical alignment is maintained, driving is carried out by using a lateral electric field so that an alignment direction of liquid crystal molecules is defined. In the display mode, a pixel configuration is simple because alignment control by a rib as in the MVA mode is not necessary. Further, the display mode has an excellent viewing angle characteristic.
Patent Documents 3 and 4 disclose that: a bent electric field is formed by electric field application; two domains having liquid crystal directors in directions different from each other by 180 degrees are formed; and, as a result, a wide viewing angle is obtained.
However, the display mode described above has a serious problem such that a driving voltage is high and a light transmittance is low, though having a high contrast and an excellent viewing angle characteristic as described above. Further, as in the MVA mode, a response characteristic of the display mode is not sufficient for moving image display. Therefore, this display mode has not been put to practical use yet.
Therefore, there has been no known liquid crystal panel and liquid crystal display device each of which can simultaneously achieve characteristics of a high-speed response, a wide viewing angle, and a high contrast.